1. Field of the Invention
The present invention relates to a method and hearing aid for enhancing the accuracy of sounds heard by a hearing-impaired listener; more particularly, the present invention relates to a method and hearing aid for enhancing the accuracy of sounds heard by a hearing-impaired listener by means of modifying the frequency of an input sound.
2. Description of the Related Art
Hearing aids have existed for decades. The main concept of the hearing aid is to amplify the sound so as to help a hearing-impaired listener to hear the previously-unheard sound. As a result, the hearing-impaired listener can hear the voice of a speaker without the need for the speaker to intentionally speak louder. However, hearing aids do not allow the hearing impaired listener to hear all sounds. Types of sounds that hearing-impaired listeners cannot hear have two characteristics: the frequency is too high, and the intensity is too low. Sounds with these two characteristics are often undetected by the hearing-impaired listener. For example, because the Mandarin consonants “”, “” and “” have such characteristics, the hearing-impaired listener has trouble hearing these syllables. However, most conventional hearing aids, which are used only for enhancing the energy of the overall sound without identifying individual phonemes that need to be enhanced, may distort the sounds during amplification. Related known prior arts regarding improving the sound by processing the frequency are briefly described hereinafter:
U.S. Pat. No. 7,305,100 discloses a “dynamic compression in a hearing aid” mainly used for minimizing sound delay.
U.S. Pat. No. 4,454,609 discloses a “speech intelligibility enhancement” used for enhancing the consonant sounds of speech with high frequencies. The greater the high-frequency content relative to the low, the more the high-frequency content is boosted. In this known prior art, high-frequency consonant sounds are enhanced. However, it is very difficult to detect the occurrence of consonants in daily conversations. Therefore, this known prior art is not applicable to a hearing aid.
U.S. Pat. No. 4,759,071 discloses an “automatic noise eliminator for hearing aids” mainly used for noise elimination. It removes all sounds below a predetermined level and transmits a compressed sound range for all sounds above a predetermined level. The object of this known prior art is different from that of the present invention. Further, it may cause sound distortion by removing all sounds below the predetermined level.
U.S. Pat. No. 6,577,739 discloses an “apparatus and methods for proportional audio compression and frequency shifting”, which provides an understandable audio signal to listeners who have hearing loss in particular frequency ranges by proportionally compressing the audio signal. However, this known prior art compresses all audio signals, which may result in serious sound distortion.
U.S. Pat. No. 7,609,841 (hereinafter as “the '841 patent”) discloses a “frequency shifter for use in adaptive feedback cancellers for hearing aids”, which improves a conventional frequency shifting method by means of applying frequency shifting only to the high frequency portion of the signal (which is shifted alternately upward and/or downward), wherein the frequency shifting ratio is less than 6%. Although the '841 patent also applies frequency shifting to high frequency signals, its frequency shifting intensity and frequency shifting direction are different from those of the present invention.
U.S. Pat. No. 7,580,536 (hereinafter “the '536 patent”) discloses a “sound enhancement for hearing-impaired listeners”, which provides a method of enhancing the sound heard by a hearing-impaired listener. The '536 patent compresses high frequency sounds with energy greater than a predetermined threshold or shifts the high frequency sounds to a lower frequency range without altering low frequency sounds (such as normal human speaking frequencies). According to the embodiment of the '536 patent, the processed high frequency sounds are at 32 kHz (column 6, line 18), which is not a normal human speaking frequency. Further, the specification of the '536 patent does not disclose the value of the “predetermined threshold”.
Therefore, there is a need to provide a method and hearing aid for enhancing the accuracy of sounds heard by a hearing-impaired listener capable of identifying the sound that needs to be enhanced so as to modify the frequency accordingly, thereby mitigating and/or obviating the aforementioned problems.